Multi-metallic ziegler-natta procatalysts and cataysts prepared therefrom for olefin polymerizations

ABSTRACT

Novel catalyst compositions comprising three or more transition metals are effective in increasing catalyst efficiency, reducing polydispersity, and increasing uniformity in molecular weight distribution when used in olefin, and particularly, linear low density polyethylene (LLDPE), polymerizations. The resulting polymers may be used to form differentiated products including, for example, films that may exhibit improved optical and mechanical properties.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a non-provisional application claiming priority fromthe U.S. Provisional Patent Application No. 61/491,924 filed on Jun. 1,2011, entitled “MULTI-METALLIC ZIEGLER-NATTA PROCATALYSTS AND CATALYSTSPREPARED THEREFROM FOR OLEFIN POLYMERIZATIONS,” the teachings of whichare incorporated by reference herein, as if reproduced in fullhereinbelow.

BACKGROUND

1. Field of the Invention

The invention relates to Ziegler-Natta catalysts useful for olefinpolymerizations. More particularly, it relates to multi-metallicZiegler-Natta catalysts showing improved efficiency and properties inproduction of ethylene based polymers such as linear low densitypolyethylene (LLDPE) polymers in particular.

2. Background of the Art

Currently the demand for polyethylene worldwide is in excess of 80million metric tons per year. Because there is a need for significantand continued differentiation of polymer products in the polyethylenebusiness, researchers have devoted a great deal of effort to searchingfor process alterations that will yield such new products. One focusinvolves exploring new catalysts.

Ziegler-Natta catalysts have been used for many years in producing avariety of polyethylenes, including LLDPE. These catalysts generallyinclude a magnesium halide support and one or two transition metalcompounds. Though effective, these catalysts frequently result in LLDPEresins with broad polydispersity and undesirably broad short chainbranching distribution (SCBD).

In LLDPE production, ethylene is generally copolymerized with ashort-chain olefin comonomer (for example, 1-butene, 1-hexene and/or1-octene). The resulting polymer is substantially linear but includessignificant numbers of short branches, and these characteristics give ita higher tensile strength, higher impact strength and higher punctureresistance than those of low density polyethylene (LDPE). These improvedproperties, in turn, mean that lower thickness (gauge) films can beblown and the product exhibits improved environmental stress crackingresistance. LLDPE is used predominantly in film applications due to itstoughness, flexibility and relative transparency. Product examples rangefrom agricultural films, food protection wrap, and bubble wrap, tomultilayer and composite films. Unfortunately, LLDPE tends to besomewhat more difficult overall to process than LDPE and may also beless tough and/or exhibit some less desirable optical properties.

In view of the above deficits in the performance of many known LLDPEpolymers, it is desirable to identify process and/or compositional meansand methods which can be employed in producing new, differentiated LLDPEpolymers. Furthermore, it is desirable that such new means and/ormethods offer process and product advancements such as enhanced catalystefficiencies, narrower polydispersities, and narrower SCBD for improveduniformity of such products.

SUMMARY OF THE INVENTION

In a first embodiment, the present invention provides a process toprepare a tri-metallic procatalyst comprising (a) reacting ahydrocarbon-soluble organomagnesium compound or complex thereof and anactive non-metallic or metallic halide to form a halogenated magnesiumsupport; b) contacting the magnesium halide support with a conditioningcompound containing an element selected from the group consisting ofboron, aluminum, gallium, indium and tellurium under conditionssufficient to form a conditioned magnesium halide support; (c)contacting the conditioned magnesium halide support and a compoundcontaining, as a first metal, titanium, to form a supported titaniumcompound; (d) contacting the supported titanium compound and a secondmetal and a third metal independently selected from the group consistingof zirconium, hafnium, vanadium, niobium, tantalum, chromium,molybdenum, and tungsten, provided that the second metal and the thirdmetal are not the same; and further provided that the molar ratio of themagnesium to a combination of the titanium and the second and thirdmetals ranges from 30:1 to 5:1; under conditions sufficient to form amulti-metallic procatalyst.

In a second embodiment, the present invention provides a multi-metallicprocatalyst obtained according to the above process described in theabove first embodiment.

In a third embodiment, the present invention provides a multi-metallicpolymerization catalyst comprising the reaction product of themulti-metallic procatalyst as described above and an organometalliccocatalyst.

In a fourth embodiment, the present invention provides a polyethylenepolymer prepared by a process wherein ethylene and optionally one ormore olefin comonomers are polymerized in the presence of thetri-metallic polymerization catalyst, as described above.

In yet another aspect the invention provides an LLDPE polymer having apolydispersity of less than 3.50, optionally a high density fraction ofless than 25 weight percent, and a molecular weight at comonomer contentratio (MWCCR) in the range of 0.75 to 1.1.

In still another aspect the invention provides an LLDPE polymer preparedby a process wherein the procatalyst composition described hereinaboveis contacted with an organometallic cocatalyst such that a catalyst isformed; ethylene; and an olefin co-monomer; under conditions such thatan LLDPE polymer having the above properties is formed.

In yet another aspect the invention provides an article prepared fromthis LLDPE polymer.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The catalyst compositions of the invention may be defined herein asbeing at least trimetallic, but may also include more than threetransition metals, and thus may in one embodiment be defined morecomprehensively as multi-metallic. These three, or more, transitionmetals are specifically selected prior to production of the catalyst.While a wide variety of combinations is possible, all catalysts used inthe invention include titanium as one element.

The catalyst compositions may be prepared beginning first withpreparation of a conditioned magnesium halide based support. Preparationof a conditioned magnesium halide based support begins with selecting anorganomagnesium compound or a complex including an organomagnesiumcompound. Such compound or complex is desirably soluble in an inerthydrocarbon diluent. The concentrations of components are preferablysuch that when the active halide, such as a metallic or non-metallichalide, and the magnesium complex are combined, the resultant slurry isfrom about 0.005 to about 0.2 molar (moles/liter) with respect tomagnesium. Examples of suitable inert organic diluents include liquefiedethane, propane, isobutane, n-butane, n-hexane, the various isomerichexanes, isooctane, paraffinic mixtures of alkanes having from 5 to 10carbon atoms, cyclohexane, methylcyclopentane, dimethylcyclohexane,dodecane, industrial solvents composed of saturated or aromatichydrocarbons such as kerosene, naphthas, and combinations thereof,especially when freed of any olefin compounds and other impurities, andespecially those having boiling points in the range from about −50° C.to about 200° C. Also included as suitable inert diluents areethylbenzene, cumene, decalin and combinations thereof.

Suitable organomagnesium compounds and complexes may include, forexample, magnesium C2-C8 alkyls and aryls, magnesium alkoxides andaryloxides, carboxylated magnesium alkoxides, and carboxylated magnesiumaryloxides. Preferred sources of magnesium moieties may include themagnesium C2-C8 alkyls and C1-C4 alkoxides. Such organomagnesiumcompound or complex may be reacted with a metallic or non-metallichalide source, such as a chloride, bromide, iodide, or fluoride, inorder to make a magnesium halide compound under suitable conditions.Such conditions may include a temperature ranging from −25° C. to 100°C., preferably 0° C. to 50° C.; a time ranging from 1 to 12 hours,preferably from 4 to 6 hours; or both. The result is a magnesium halidebased support.

The magnesium halide support is then reacted with a selectedconditioning compound containing an element selected from the groupconsisting of boron, aluminum, gallium, indium and tellurium, underconditions suitable to form a conditioned magnesium halide support. Thiscompound and the magnesium halide support are then brought into contactunder conditions sufficient to result in a conditioned magnesium halidesupport. Such conditions may include a temperature ranging from 0° C. to50° C., preferably from 25° C. to 35° C.; a time ranging from 4 to 24hours, preferably from 6 to 12 hours; or both. Without wishing to bebound by any theory of mechanism, it is suggested that this aging servesto facilitate or enhance adsorption of additional metals onto thesupport.

Once the conditioned support is prepared and suitably aged, it isbrought into contact with a titanium compound. In certain preferredembodiments titanium halides or alkoxides, or combinations thereof, maybe selected. Conditions may include a temperature within the range from0° C. to 50° C., preferably from 25° C. to 35° C.; a time from 3 hoursto 24 hours, preferably from 6 hours to 12 hours; or both. The result ofthis step is adsorption of at least a portion of the titanium compoundonto the conditioned magnesium halide support.

Finally, two additional metals, referred to herein as “the second metal”and “the third metal” for convenience, will also be adsorbed onto themagnesium based support, The “second metal” and the “third metal” areindependently selected from zirconium (Zr), hafnium (Hf), vanadium (V),niobium (Nb), tantalum (Ta), chromium (Cr), molybdenum (Mo), andtungsten (W). These metals may be incorporated in any of a variety ofways known to those skilled in the art, but generally contact betweenthe conditioned magnesium based halide support including titanium andthe selected second and third metals, in, e.g., liquid phase such as anappropriate hydrocarbon solvent, will be suitable to ensure depositionof the additional metals to form what may now be referred to as the“procatalyst,” which is a multi-metallic procatalyst.

The multi-metallic procatalyst has a molar ratio constitution that isspecific and which is believed to be an important feature in ensuringthe desirable polymer properties that may be attributed to the catalystmade from the procatalyst. Specifically, the procatalyst desirablyexhibits a molar ratio of the magnesium to a combination of the titaniumand the second and third metals that ranges from 30:1 to 5:1; underconditions sufficient to form a multi-metallic procatalyst. Thus, theoverall molar ratio of magnesium to titanium ranges from 8:1 to 80:1.

Once the procatalyst has been formed, it may be used to form a finalcatalyst by combining it with a cocatalyst consisting of at least oneorganometallic compound such as an alkyl or haloalkyl of aluminum, analkylaluminum halide, a Grignard reagent, an alkali metal aluminumhydride, an alkali metal borohydride, an alkali metal hydride, analkaline earth metal hydride, or the like. The formation of the finalcatalyst from the reaction of the procatalyst and the organometalliccocatalyst may be carried out in situ, or just prior to entering thepolymerization reactor. Thus, the combination of the cocatalyst and theprocatalyst may occur under a wide variety of conditions. Suchconditions may include, for example, contacting them under an inertatmosphere such as nitrogen, argon or other inert gas at temperatures inthe range from 0° C. to 250° C., preferably from 15° C. to 200° C. Inthe preparation of the catalytic reaction product, it is not necessaryto separate hydrocarbon soluble components from hydrocarbon insolublecomponents. Time for contact between the procatalyst and cocatalyst maydesirably range, for example, from 0 to 240 seconds, preferably from 5to 120 seconds. Various combinations of these conditions may beemployed.

Once the catalyst compositions of the invention have been prepared, theyare suitable to use for olefin polymerizations. In particularembodiments these are slurry (wherein the polymer is not dissolved inthe carrier) or solution (wherein the temperature is high enough tosolubilize the polymer in the carrier) polymerizations, or the like, toprepare LLDPE. In general this may be carried out generally in areaction medium, such as an isoparaffin or other aliphatic hydrocarbondiluents, with the olefin, or a combination of olefins, being broughtinto contact with the reaction medium in the presence of the selectedcatalyst, preferably as the sole catalyst. Conditions may be any thatare suitable, and a molecular weight regulator, frequently hydrogen, isoften present in the reaction vessel in order to suppress formation ofundesirably high molecular weight polymers.

The polymers of the present invention can be homopolymers of C2-C20alpha-olefins, such as ethylene, propylene, or 4-methyl-1-pentene, orthey may be interpolymers of ethylene or propylene with at least one ormore alpha-olefins and/or C2-C20 acetylenically unsaturated monomersand/or C4-C18 diolefins. They may also be interpolymers of ethylene withat least one of the above C3-C20 alpha-olefins, diolefins and/oracetylenically unsaturated monomers in combination with otherunsaturated monomers. Those skilled in the art will understand thatselected monomers are desirably those that do not destroy conventionalZiegler-Natta catalysts. For example, in one embodiment ethylene or amixture of ethylene and from about 0.1 to about 20 weight percent (wt%), for example, from about 0.1 to about 15 wt %, or in the alternative,from about 0.1 to about 10 wt %; or in the alternative, from 0.1 toabout 5 weight percent of 1-hexene, 1-octene, or a similar higherα-olefin, based on total monomer in the final copolymer, may besuccessfully polymerized using the inventive process.

In the polymerization process employing the aforementioned catalyticreaction product, polymerization is effected by adding a catalyticamount of the inventive catalyst composition to a polymerization reactorcontaining the selected α-olefin monomer, or vice versa. Thepolymerization reactor is maintained at temperatures in the range from150° C. to 300° C., preferably at solution polymerization temperatures,e.g., from 150° C. to 250° C., for a residence time, in certainnon-limiting embodiments, ranging from 5 minutes to 20 minutes. Longeror shorter residence times may alternatively be employed. It isgenerally desirable to carry out the polymerization in the absence ofmoisture and oxygen and in the presence of a catalytic amount of thecatalytic reaction product that is typically within the range from0.0001 to about 0.01 milligram-atoms transition metal per liter ofdiluent. It is understood, however, that the most advantageous catalystconcentration will depend upon polymerization conditions such astemperature, pressure, solvent and the presence of catalyst poisons andthat the foregoing range is given for illustrative purposes of oneparticular but non-limiting embodiment only.

For example, pressures may be relatively low, e.g., from 150 to 3,000psig (1.0 to 20.7 MPa), preferably from 250 to 1,000 psig (1.7 to 6.9MPa), most preferably from 450 to 800 psig (3.1 to 5.5 MPa). However,polymerization within the scope of the invention can occur at pressuresfrom atmospheric up to pressures determined by the capabilities of thepolymerization equipment.

Generally in the polymerization process, a carrier which may be an inertorganic diluent or solvent or excess monomer is generally employed.Generally care is desirably taken to avoid oversaturation of the solventwith polymer. If such saturation occurs before the catalyst becomesdepleted, the full efficiency of the catalyst may not be realized. Inparticular embodiments, it may be preferable that the amount of polymerin the carrier not exceed 30 percent, based on the total weight of thereaction mixture. It may also be very desirable to stir thepolymerization components in order to attain desirable levels oftemperature control and to enhance the uniformity of the polymerizationthroughout the polymerization zone. For example, in the case ofrelatively more rapid reactions with relatively active catalysts, meansmay be provided for refluxing monomer and diluent, if diluent isincluded, thereby removing some of the the heat of reaction. In anyevent, adequate means should be provided for dissipating the exothermicheat of polymerization. Thus, polymerization may be effected in a batchmanner, or in a continuous manner, such as, for example, by passing thereaction mixture through an elongated reaction tube which is contactedexternally with suitable cooling medium to maintain the desired reactiontemperature, or by passing the reaction mixture through an equilibriumoverflow reactor or a series of the same.

In order to enhance catalyst efficiency in the polymerization ofethylene, it may also be desirable to maintain a certain ethyleneconcentration in the diluents in order to ensure reactor stability and,preferably, optimize catalyst efficiency. In some embodiments this mayinclude a ratio of solvent to ethylene ranging from 1:2 to 1:8,preferably 1:3 to 1:5. To achieve this when an excess of ethylene is fedinto the system, a portion of the ethylene can be vented.

Hydrogen is often employed in the practice of this invention, for thepurpose of lowering the molecular weight of the resultant polymer. Forthe purpose of the invention, it is beneficial to employ hydrogen in thepolymerization mixture in concentrations ranging preferably from 0.001to 1 mole per mole of monomer. The larger amounts of hydrogen withinthis range may be useful to produce generally lower molecular weightpolymer. It is generally known to those skilled in the art that hydrogenmay be added to the polymerization vessel either with a monomer stream,or separately therefrom, before, during or after addition of the monomerto the polymerization vessel. However, in preferred embodiments it ishighly desirable to ensure that the hydrogen is added either before orduring addition of the catalyst, in the range of from 200,000 to 3million grams of polymer per gram of Ti, such as, for example, from600,000 to 2 million grams of polymer per gram of Ti.

The resulting polymer may be effectively recovered from thepolymerization mixture by driving off unreacted monomer and diluent,where such is employed. No further removal of impurities is required.The resultant polymer may contain small amounts of catalyst residue asshown in the succeeding examples and also possess a relatively narrowmolecular weight distribution. The resulting polymer may further be meltscreened. Subsequent to the melting process in the extruder, the moltencomposition is passed through one or more active screens, positioned inseries of more than one, with each active screen having a micronretention size of from about 2 μm to about 400 μm (2 to 4×10⁻⁵ m), andpreferably about 2 μm to about 300 μm (2 to 3×10⁻⁵ m), and mostpreferably about 2 μm to about 70 μm (2 to 7×10⁻⁶ m), at a mass flux ofabout 5 to about 100 lb/hr/in² (1.0 to about 20 kg/s/m²). Such furthermelt screening is disclosed in U.S. Pat. No. 6,485,662, which isincorporated herein by reference to the extent that it discloses meltscreening.

The resulting polymer may, in certain particularly preferredembodiments, be prepared such that it has properties that include apolydispersity of less than 3.50 and a MWCCR of less than 1.10,preferably from 0.75 to 1.10. The resulting polymer may optionally havea high density fraction of less than 25 weight percent.

The polyethylene composition according to instant invention has adensity in the range of 0.900 to 0.960 g/cm³. All individual values andsubranges from 0.900 to 0.960 g/cm³ are included herein and disclosedherein; for example, the density can be from a lower limit of 0.900,0.911, 0.919, 0.923, 0.928, or 0.936 g/cm³ to an upper limit of 0.941,0.947, 0.954, 0.959, or 0.960, g/cm³. For example, the polyethylenecomposition may have a density in the range of 0.905 to 0.945 g/cm³; orin the alternative, the polyethylene composition may have a density inthe range of 0.910 to 0.935 g/cm³; or in the alternative, thepolyethylene composition may have a density in the range of from 0.915to 0.925 g/cm³.

The polyethylene composition according to the instant invention has amolecular weight distribution (M_(w)/M_(n)) (measured according to theconventional GPC method) in the range of 2.6 to 4.2. All individualvalues and subranges from 2.6 to 4.2 are included herein and disclosedherein; for example, the molecular weight distribution (M_(w)/M_(n)) canbe from a lower limit of 2.6, 2.8, 3.0, 3.2, or 3.3 to an upper limit of2.8, 3.0, 3.2, 3.3, 3.8, or 4.2. In non-limiting example, thepolyethylene composition may have a molecular weight distribution(M_(w)/M_(n)) in the range of from 2.6 to 3.6; or in the alternative,the polyethylene composition may have a molecular weight distribution(M_(w)/M_(n)) in the range of from 2.6 to 3.2.

The polyethylene composition according to the instant invention has amelt index (I₂) in the range of 0.1 to 50 g/10 minutes. All individualvalues and subranges from 0.1 to 50 g/10 minutes are included herein anddisclosed herein; for example, the melt index (I₂) can be from a lowerlimit of 0.1, 0.5, 0.8, 1, 2, 3, 5, 6, 7, or 8 g/10 minutes, to an upperlimit of 0.5, 0.8, 1, 2, 3, 5, 6, 7, 8, or 10 g/10 minutes. Innon-limiting example, the polyethylene composition may have a melt index(I₂) in the range of from 0.2 to 20 g/10 minutes; or in the alternative,the polyethylene composition may have a melt index (I₂) in the range offrom 0.5 to 5 g/10 minutes.

The polyethylene composition according to the instant invention has amelt flow ratio (I₁₀/I₂) in the range of from 6 to 12. All individualvalues and subranges from 6 to 12 are included herein and disclosedherein; for example, the melt flow ratio (I₁₀/I₂) can be from a lowerlimit of 6, 7, 8, 9, 10, or 11 to an upper limit of 7, 8, 9, 10, 11, or12. For example, the polyethylene composition may have a melt flow ratio(I₁₀/I₂) in the range of from 6 to 10; or in the alternative, thepolyethylene composition may have a melt flow ratio (I₁₀/I₂) in therange of from 6.5 to 8.

The polyethylene composition according to the instant invention has amolecular weight (M_(w)) in the range of 50,000 to 300,000 daltons.

The polyethylene composition may have a molecular weight at densityratio (MWCCR) in the range of from 0.75 to 1.10. All individual valuesand subranges from 0.75 to 1.10 are included herein and disclosedherein; for example, the polyethylene composition may have a MWCCR inthe range of from 0.75, 0.80, 0.85, 0.90, 1.0, or 1.05 to 0.80, 0.85,0.90, 1.0, or 1.1. The polyethylene composition may have a vinylunsaturation in the range of 0.10 to 0.50 vinyls per one thousand carbonatoms present in the backbone of the polyethylene composition. Allindividual values and subranges from 0.15 to 0.35 are included hereinand disclosed herein; for example, the polyethylene composition may havea vinyl unsaturation of less than 0.20 vinyls per one thousand carbonatoms present in the backbone of the polyethylene composition; or in thealternative, the polyethylene composition may have a vinyl unsaturationof less than 0.30 vinyls per one thousand carbon atoms present in thebackbone of the polyethylene composition.

The polyethylene composition may comprise less than 20 percent by weightof units derived from one or more α-olefin comonomers. All individualvalues and subranges from less than 20 weight percent are includedherein and disclosed herein; for example, the polyethylene compositionmay comprise less than 15 percent by weight of units derived from one ormore α-olefin comonomers; or in the alternative, the polyethylenecomposition may comprise less than 12 percent by weight of units derivedfrom one or more α-olefin comonomers; or in the alternative, thepolyethylene composition may comprise less than 9 percent by weight ofunits derived from one or more α-olefin comonomers; or in thealternative, the polyethylene composition may comprise less than 7percent by weight of units derived from one or more α-olefin comonomers;or in the alternative, the polyethylene composition may comprise lessthan 5 percent by weight of units derived from one or more α-olefincomonomers; or in the alternative, the polyethylene composition maycomprise less than 3 percent by weight of units derived from one or moreα-olefin comonomers; or in the alternative, the polyethylene compositionmay comprise less than 1 percent by weight of units derived from one ormore α-olefin comonomers; or in the alternative, the polyethylenecomposition may comprise less than 0.5 percent by weight of unitsderived from one or more α-olefin comonomers.

The α-olefin comonomers typically have no more than 20 carbon atoms. Forexample, the α-olefin comonomers may preferably have 3 to 10 carbonatoms, and more preferably 3 to 8 carbon atoms. Exemplary α-olefincomonomers include, but are not limited to, propylene, 1-butene,1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene, and4-methyl-1-pentene. The one or more α-olefin comonomers may, forexample, be selected from the group consisting of propylene, 1-butene,1-hexene, and 1-octene; or in the alternative, from the group consistingof 1-hexene and 1-octene.

The polyethylene composition may comprise at least 80 percent by weightof units derived from ethylene. All individual values and subranges fromat least 80 weight percent are included herein and disclosed herein; forexample, the polyethylene composition may comprise at least 88 percentby weight of units derived from ethylene; or in the alternative, thepolyethylene composition may comprise at least 89 percent by weight ofunits derived from ethylene; or in the alternative, the polyethylenecomposition may comprise at least 91 percent by weight of units derivedfrom ethylene; or in the alternative, the polyethylene composition maycomprise at least 93 percent by weight of units derived from ethylene;or in the alternative, the polyethylene composition may comprise atleast 95 percent by weight of units derived from ethylene; or in thealternative, the polyethylene composition may comprise at least 97percent by weight of units derived from ethylene; or in the alternative,the polyethylene composition may comprise at least 99 percent by weightof units derived from ethylene; or in the alternative, the polyethylenecomposition may comprise at least 99.5 percent by weight of unitsderived from ethylene.

The polyethylene composition of the instant invention is substantiallyfree of any long chain branching, and preferably, the polyethylenecomposition of the instant invention is free of any long chainbranching. Substantially free of any long chain branching, as usedherein, refers to a polyethylene composition preferably substituted withless than about 0.01 long chain branching per 1000 total carbons, andmore preferably, less than about 0.001 long chain branching per 1000total carbons. In the alternative, the polyethylene composition of theinstant invention is free of any long chain branching.

The polyethylene composition may further comprise greater than or equalto 1 parts by combined weight of at least three metal residues remainingfrom the multi-metallic polymerization catalyst per one million parts ofpolyethylene composition, where such metals are selected from the groupconsisting of titanium, zirconium, hafnium, vanadium, niobium, tantalum,chromium, molybdenum, tungsten, and combinations thereof, wherein eachmetal residual is present at least 0.4 ppm, for example, in the range offrom 0.4 to 5 ppm. All individual values and subranges from greater thanor equal to 1 ppm are included herein and disclosed herein; for example,the polyethylene composition may further comprise greater than or equalto 2 parts by combined weight of at least three metal residues remainingfrom the multi-metallic polymerization catalyst per one million parts ofpolyethylene composition. The at least three metals residues remainingfrom the multi-metallic polymerization catalyst in the inventivepolyethylene composition may be measured by x-ray fluorescence (XRF),which is calibrated to reference standards. The polymer resin granuleswere compression molded at elevated temperature into plaques having athickness of about ⅜ of an inch for the x-ray measurement in a preferredmethod. At very low concentrations of metal, such as below 0.1 ppm,ICP-AES would be a suitable method to determine metal residues presentin the inventive polyethylene composition.

In one embodiment, the polyethylene composition in accordance with theinstant invention may have 2 or more peaks on an elutiontemperature-eluted amount curve determined by continuous temperaturerising elution fraction method at equal or above 30° C., wherein thepurge peak which is below 30° C. is excluded.

The inventive polyethylene composition may further comprise additionalcomponents such as other polymers and/or additives. Such additivesinclude, but are not limited to, antistatic agents, color enhancers,dyes, lubricants, fillers, pigments, primary antioxidants, secondaryantioxidants, processing aids, UV stabilizers, and combinations thereof.The inventive polyethylene composition may contain any amounts ofadditives. The inventive polyethylene composition may comprise fromabout 0 to about 10 percent by the combined weight of such additives,based on the weight of the inventive polyethylene composition includingsuch additives. All individual values and subranges from about 0 toabout 10 weight percent are included herein and disclosed herein; forexample, the inventive polyethylene composition may comprise from 0 to 7percent by the combined weight of additives, based on the weight of theinventive polyethylene composition including such additives; in thealternative, the inventive polyethylene composition may comprise from 0to 5 percent by the combined weight of additives, based on the weight ofthe inventive polyethylene composition including such additives; or inthe alternative, the inventive polyethylene composition may comprisefrom 0 to 3 percent by the combined weight of additives, based on theweight of the inventive polyethylene composition including suchadditives; or in the alternative, the inventive polyethylene compositionmay comprise from 0 to 2 percent by the combined weight of additives,based on the weight of the inventive polyethylene composition includingsuch additives; or in the alternative, the inventive polyethylenecomposition may comprise from 0 to 1 percent by the combined weight ofadditives, based on the weight of the inventive polyethylene compositionincluding such additives; or in the alternative, the inventivepolyethylene composition may comprise from 0 to 0.5 percent by thecombined weight of additives, based on the weight of the inventivepolyethylene composition including such additives. Antioxidants, such asIrgafos™ 168 and Irganox™ 1010, may be used to protect the inventivepolyethylene composition from thermal and/or oxidative degradation.Irganox™ 1010 is tetrakis (methylene(3,5-di-tert-butyl-4hydroxyhydrocinnamate) available from Ciba GeigyInc. Irgafos™ 168 is tris (2,4 di-tert-butylphenyl)phosphite availablefrom Ciba Geigy Inc.

Any conventional ethylene (co)polymerization reaction may be employed toproduce the inventive polyethylene composition. Such conventionalethylene (co)polymer-ization reactions include, but are not limited to,slurry phase polymerization process, solution phase polymerizationprocess, and combinations thereof using one or more conventionalreactors, e.g., loop reactors, stirred tank reactors, batch reactors inparallel, series, and/or any combinations thereof. In one embodiment,the polymerization reactor may comprise two or more reactors in series,parallel, or combinations thereof. In one embodiment, the polymerizationreactor is one reactor.

The polymers produced hereby may include a wide variety of productsincluding, in particular embodiments, LLDPE, but also high densitypolyethylenes (HDPE), plastomers, medium density polyethylenes,propypropylene and polypropylene copolymers. For these and otherapplications articles may be prepared showing enhanced overall qualitydue to the narrower polydispersity and narrower molecular weightdistribution of the polymer relative to density. Useful formingoperations for the polymers may include, but are not limited to, film,sheet, pipe and fiber extrusion and co-extrusion as well as blowmolding, injection molding and rotary molding may be pursued. Filmsinclude blown or cast films formed by co-extrusion or by laminationuseful as shrink film, cling film, stretch film, sealing film, orientedfilm, snack packaging, heavy duty bags, grocery sacks, baked and frozenfood packaging, medical packaging, industrial liners, agricultural filmapplications, and membranes, for example, in food-contact andnon-food-contact applications. Fibers include melt spinning, solutionspinning and melt blown fiber operations for use in woven and non-wovenform to make filters, diaper fabrics, medical garments and geotextiles.Extruded articles include medical tubing, wire and cable coatings,geomembranes and pond liners. Molded articles include single andmulti-layered constructions in the form of bottles, tanks, large hollowarticles, rigid food containers and toys.

EXAMPLES

Two samples of the invention catalysts are prepared using the protocolsgiven below (Examples 1 and 2) and three samples of non-inventioncatalysts are prepared using their protocols (Comparative Examples A-C).All five of the catalysts are then used to prepare LLDPE polymer in asolution polymerization, and then the LLDPE polymer is used to prepare ablown film. Testing is carried out on both the LLDPE polymer and theblown film, as further described hereinbelow.

Example 1

To 800 mL of MgCl₂ (0.20M in ISOPAR™ E) is added (C₂H₅)AlCl₂ (40 mL of a1.0M solution in hexane). (ISOPAR™ is a tradename of ExxonMobilChemical. ISOPAR™ E is a clear isoparaffinic fluid.) The resultingmixture is allowed to stir overnight at room temperature. Solutions ofTiCl₄ (16 mL of a 0.25M solution in ISOPAR™ E) and VOCl₃ (32 mL of a0.25M solution in ISOPAR™ E) are mixed and then added to themagnesium/aluminum suspension, followed by a solution of Zr(TMHD)₄(bis(2,2,6,6-tetramethyl-3,5-heptanedionate)zirconium, 8 mL of a 0.25Msolution in ISOPAR™ E). The resulting mixture is allowed to stirovernight to complete the procatalyst aging.

Example 2

To 800 mL of MgCl₂ (0.20M in ISOPAR™ E) is added (C₂H₅)AlCl₂ (24 mL of a1.0M solution in hexane). The resulting mixture is allowed to stirovernight at room temperature. Solutions of TiCl₄ (16 mL of a 0.25Msolution in ISOPAR™ E) and VOCl₃ (32 mL of a 0.25M solution in ISOPAR™E) are mixed and then added to the magnesium/aluminum suspension,followed by a solution of Hf(TMHD)₄(bis(2,2,6,6-tetramethyl-3,5-heptanedionate)hafnium, 8 mL of a 0.25Msolution in ISOPAR™ E). The resulting mixture is allowed to stirovernight to complete the procatalyst aging.

Comparative Example A

To 800 mL of MgCl₂ (0.20M in ISOPAR™ E) is added (C₂H₅)AlCl₂ (48 mL of a1.0M solution in hexane). The resulting mixture is allowed to stirovernight at room temperature. A solution of Ti(OiPr)₄ (titaniumisopropoxide, 48 mL of a 0.25M solution in ISOPAR™ E) is then added tothe magnesium/aluminum suspension. The resulting mixture is allowed tostir overnight to complete the procatalyst aging.

Comparative Example B

To 800 mL of MgCl₂ (0.20M in ISOPAR™ E) is added (C₂H₅)AlCl₂ (32 mL of a1.0M solution in hexane). The resulting mixture is allowed to stirovernight at room temperature. A solution of TiCl₄ (16 mL of a 0.25Msolution in ISOPAR™ E) is then added to the magnesium/aluminumsuspension. The resulting mixture is allowed to stir overnight tocomplete the procatalyst aging.

Comparative Example C

To 800 milliters (mL) of MgCl₂ (0.20M in ISOPAR™ E) is added (C₂H₅)AlCl₂(32 mL of a 1.0M solution in hexane). The resulting mixture is allowedto stir overnight at room temperature. Solutions of titanium chloride(TiCl₄) (16 mL of a 0.25M solution in ISOPAR™ E) and VOCl₃ (32 mL of a0.25M solution in ISOPAR™ E) are mixed and then added to themagnesium/aluminum suspension. The resulting mixture is allowed to stirovernight to complete the procatalyst aging.

Each of the catalysts prepared hereinabove is then used to prepare LLDPEpolymer via a typical solution polymerization method. In this methodthree feeds—ethylene, hydrogen, and octene—are fed at a rate as shown inTable 1 hereinbelow into a polymerization zone maintained at atemperature of 185° C. The three flow rates are adjusted in order toproduce a copolymer with a target I₂ of 1.0 and a density of 0.920g/cm³.

As shown in Table 1, Example 1 and 2 both show improved catalystefficiency (EFF) when compared with that of Comparative Examples A andB. Example 1 and 2 also show significantly narrower polydispersity (PDIless than 3.5, Table 1) in comparison with the Comparative Examples, andalso lower molecular weight at density ratio (M_(w) of high densityfraction to M_(w) of low density fraction, Table 2).

Number and weight-average molecular weights (M_(n) and M_(w),respectively) and polydispersity (M_(w)/M_(n)) of the polymers aredetermined by Gel Permeation Chromatography (GPC). The column andcarousel compartments are operated at 140° C. The columns are 4 PL GelMixed B 10-micron columns. The solvent is 1,2,4-trichlorobenzene. Thesamples are prepared at a concentration of 0.1 g of polymer in 50 mL ofsolvent. The chromatographic solvent and the samples preparation solventcontains 200 ppm of butylated hydroxytoluene (BHT). Both solvent sourcesare nitrogen sparged. The samples are stirred for 2 hours at 160° C. Theinjection volume is 100 μL and the flow rate is 1.0 mL/min.

Gel Permeation Chromatography (GPC)

Number and weight-average molecular weights (M_(n) and M_(w),respectively) and polydispersity (M_(w)/M_(n)) of the polymers aredetermined by Gel Permeation Chromatography (GPC). The chromatographicsystem consists of either a Polymer Laboratories Model PL-210 or aPolymer Laboratories Model PL-220 high temperature chromatograph. Datacollection is accomplished using Viscotek (Housten, Tex.) TriSECsoftware version 3 and a 4-channel Viscotek Data Manager DM400. Thesystem is equipped with an on-line solvent degas device from PolymerLaboratories.

The column and carousel compartments are operated at 140° C. The columnsused are 4 PL Gel Mixed B 10-micron columns. The solvent used is1,2,4-trichlorobenzene. The samples are prepared at a concentration of0.1 g of polymer in 50 mL of solvent. The chromatographic solvent andthe samples preparation solvent contain 200 ppm of butylatedhydroxytoluene (BHT). Both solvent sources are nitrogen sparged. Thesamples are stirred for 2 hours at 160° C. The injection volume used is100 μL and the flow rate is 1.0 mL/min. Calibration of the GPC columnset is performed with narrow MWD polystyrene standards with molecularweights ranging from 580 to 8,400,000 g/mol, purchased from PolymerLaboratories (Shropshire, UK). Data reduction is performed with ViscotekTriSEC software. The polystyrene standard peak molecular weights areconverted to polyethylene molecular weights using the method disclosedin Williams, T., and Ward, I. M., “The Construction of PolyethyleneCalibration Curve for Gel Permeation Chromatography Using PolystyreneFractions”, J. Polym. Sci. Polym. Lett., 6, 621 (1968):

M _(polyethylene) =A(M _(polystyrene))^(B)

wherein M is the molecular weight, A has a value of 0.4316 and B isequal to 1.0. Polyethylene equivalent molecular weight calculations areperformed using Viscotek TriSEC software Version 3.0.

CEF Method

Comonomer distribution analysis is performed with CrystallizationElution Fractionation (CEF). The method includes first combiningortho-dichlorobenzene (ODCB) with 600 ppm antioxidant butylatedhydroxytoluene (BHT) used as solvent. Samples are prepared using anautosampler at 160° C. for 2 hours under shaking at 4 mg/mL). Theinjection volume is 300 microliters. The temperature profile used forthe CEF is as follows: Crystallization at 3° C./min from 110° C. to 30°C.; thermal equilibrium at 30° C. for 5 minutes; and elution at 3°C./min from 30° C. to 140° C. The flow rate during crystallization is0.052 mL/min and during elution 0.50 mL/min. The data is collected atone data point/second.

A CEF column is packed with acid-washed glass beads at 125 um±6% s with⅛ inch stainless tubing. Column volume is 2.06 mL. Column temperaturecalibrations are performed using a mixture of NIST Standard ReferenceMaterial Linear polyethylene 1475a (1.0 mg/mL) and Eicosane (2 mg/mL) inODCB. Temperature is calibrated by adjusting elution heating rate sothat NIST linear polyethylene 1475a has a peak temperature at 101.0° C.,and Eicosane has a peak temperature of 30.0° C. The CEF columnresolution is calculated with a mixture of NIST linear polyethylene1475a (1.0 mg/ml) and hexacontane (≧97.0% purity, 1 mg/mL). A baselineseparation of hexacontane and NIST polyethylene 1475a is achieved. Thearea of hexacontane (from 35.0° C. to 67.0° C.) to the area of NIST1475a from 67.0° C. to 110.0° C. is determined to be 50:50, with theamount of soluble fraction below 35° C. being less than 1.8 wt %. Columnresolution is 6.0.

${Resolution} = \frac{\begin{matrix}{{{Peak}\mspace{14mu} {Temperature}\mspace{14mu} {of}{\mspace{11mu} \;}{NIST}\mspace{14mu} 1475a} -} \\{{Peak}\mspace{14mu} {Temperature}\mspace{14mu} {of}\mspace{14mu} {Hexacontane}}\end{matrix}}{\begin{matrix}{{{Half}\text{-}{weight}\mspace{14mu} {Width}\mspace{14mu} {of}\mspace{14mu} {NIST}\mspace{14mu} 1475a} +} \\{{Half}\text{-}{height}\mspace{14mu} {Width}\mspace{14mu} {of}\mspace{14mu} {Hexacontane}}\end{matrix}}$

TABLE 1 R1 Al:Ti C2 H2 C8 temp Flow Eff * Density Feed Feed Feed CEF CEFEx. ° C. g/hr 10⁶ I₂ g/cm³ kg/hr mL/min kg/hr I_(10/)I₂ % HD MWCCR PDIComp. A 185 10 0.49 1.01 0.9198 3.5 9.5 1.6 8.04 24.7 0.73 3.86 Comp. B185 9.9 0.49 1.33 0.9210 3.5 0 1.30 9.15 12.5 0.50 4.17 Comp. C 185 10.01.13 0.97 0.9198 3.5 14 1.35 7.22 19.8 0.71 3.41 Ex. 1 185 10.1 1.101.04 0.9196 3.5 23.5 1.05 6.81 24.8 0.82 3.03 Ex. 2 185 10.5 0.99 0.960.9198 3.5 12.5 1.30 7.23 22.6 0.87 3.388 I₂ Melt flow index testedaccording to ASTM D1238; dg/min (190° C., 2.16 kg) I₁₀ Melt flow indextested according to ASTM D1238; dg/min (190° C., 10 kg) I_(10/)I₂ Meltflow ratio calculated from melt flow indices I₁₀ and I₂ Density testedaccording to ASTM D792 Method B; g/cm³ PDI = weight average molecularweight/number average molecular weight (Mw/Mn)

% HD Calculation:

High density fraction The % HD is determined from the CEF plot,calculated as a weight fraction (W) of the polymer eluting betweentemperatures (T) of 93° C. to 110° C.:

$\frac{\int_{93}^{110}{{W(T)}\ {t}}}{\int_{25}^{110}{{W(T)}\ {t}}} = {\% \mspace{14mu} {HD}}$

MWCCR Calcluation:

The molecular weight at comonomer content ratio (MWCCR) is defined asthe average M_(w) of a low density fraction (eluting from 60° C. to 70°C. on the CEF plot for copolymers with densities greater than 0.910g/cc, and eluting from 30° C. to 60° C. on the CEF plot for copolymerswith densities less than 0.910 g/cc) divided the overall M_(w) of thecopolymer as determined by GPC.

For copolymers with density greater than 0.910 g/cc:

$\frac{{Mw}\left( {60{^\circ}\mspace{14mu} {C.}}\rightarrow{70{^\circ}\mspace{14mu} {C.}} \right)}{{Mw}({overall})} = {MWCCR}$

For copolymers with density less than 0.910 g/cc:

$\frac{{Mw}\left( {30{^\circ}\mspace{14mu} {C.}}\rightarrow{60{^\circ}\mspace{14mu} {C.}} \right)}{{Mw}({overall})} = {MWCCR}$

Samples of the LLDPE polymer beads prepared for Examples 1 and 2 andComparative Examples A-C are subjected to neutron activation analysis.Approximately 3.5 g of the polymer are transferred into pre-cleaned2-dram polyethylene vials. Standard aliquots of Al, Mg, Ti, V, Hf and Zrstandards are prepared from their standard solutions (National Instituteof Standards and Technology (NIST) traceable standard solutions fromSPEX CertiPrep Group) and also placed into 2-dram polyethylene vials.Each of the vials is diluted with milli-Q pure water to 6 mL and thevials are heat-sealed. The samples and standards are then analyzedfollowing the standard NAA procedure, Global-SOP-01101.01 for the givenelements, using the Mark I TRIGA™ nuclear reactor. (TRIGA™ is atradename of General Atomics.)

For Al, Mg, Ti, Hf, Zr and V analysis, the samples are transferred tonon-irradiated vials before doing the gamma-spectroscopy. The reactionsand experimental conditions used for each of the elements are asdescribed in Table 2. The elemental concentrations are calculated usingCANBERRA™ software (CANBERRA™ is a tradename of Canberra, an Areva GroupCompany) and standard comparative technique, and the results are shownin Table 3. Interference correction is carried out for the aluminuminterference with magnesium using the CANBERRA™ software.

TABLE 2 Ex. Al, ppm Mg, ppm Ti, ppm V, ppm Hf, ppm Zr, ppm Comp. A 9.2 ±0.4 17 ± 1 2.1 ± 0.1 Nd @ 0.01 Nd @ 0.02 Nd @ 0.4 Comp. B 16.0 ± 0.8  35± 2 1.4 ± 0.1 0.04 ± 0.01 Nd @ 0.02 Nd @ 0.4 Comp. C 8.5 ± 0.4 20 ± 10.97 ± 0.05 1.37 ± 0.06 Nd @ 0.02 Nd @ 0.04 Ex. 1 10.4 ± 0.5  22 ± 10.88 ± 0.05 1.62 ± 0.07 0.038 ± 0.003 0.52 + 0.05 Ex. 2 9.7 ± 0.4 26 ± 10.78 ± 0.03 2.02 ± 0.09 1.7 ± 0.2 Nd @ 0.4

The polymers produced in Examples 1 and 2 and Comparative Examples A-Care further processed via a blown film extrusion process on a Collinthree layer blown film line. The blown film line consists of threegroove fed extruders with single flight screws (25:30:25 mm). Thelength/diameter ratio for all screws is 25:1. The blown film line has a60 mm die with a dual lip air ring cooling system. The die has a die gapof 2 mm. The films are blown with a blow up ratio of 2.5 and a frostline height of 7 inches. Film thickness is 2 mil (0.05 millimeter) andlayflat width of the films is about 23.5 cm.

The products of this protocol are correspondingly labeled as Examples 3and 4 and Comparative Examples D-F. The films are then tested and theresults recorded in Table 3.

TABLE 3 Dart A CD Impact MD Tear Tear Total strength strength strengthHaze Gloss 20 Gloss 45 Example (g) (g) (g) (%) (%) (%) Comp. D 421 449578 9.1 87.8 69.4 Comp. E 286 407 538 11.1 74.9 63.4 Comp. F 607 430 5557.1 105.6 75.3 Ex. 3 571 446 558 6.5 115.6 78.6 Ex. 4 673 407 559 5.7125.0 82.5 Dart A Impact strength: per ASTM D1709, using a 1.5-inchdiameter dart head, dropped from a maximum height of 26 inches. MD andCD Tear strength: Elmendorf Tear, per ASTM D1922, based on a ProTearelectronic tear tester from Thwing-Albert. Haze: per ASTM D1003;measurements made on a Haze Gard instrument from BYD-Gardner Company.Gloss 20 and Gloss 45: per ASTM D2457.

Table 3 shows the significantly better optical properties, particularlyGloss 20 and Gloss 45, attained with the trimetallic catalyst of theinventive Examples 3 and 4 catalysts, in comparison with the mono- andbi-metallic Comparatives D-F catalysts. This improvement may beattributable to the reduced polydispersity and molecular weight atdensity ratio found in the polymers made with the catalysts. Example 4also shows improved Dart A impact strength, making the combination ofDart A impact and optical improvements, while maintaining Elmendorf tearstrength an attractive option for some applications.

What is claimed is:
 1. A polyethylene polymer prepared having apolydispersity (PDI) of less than 3.5, a MWCCR in the range of 0.75 to1.10, a density in the range of from 0.900 to 0.960 g/cm³; a melt index(I₂) in the range of from 0.1 to 50 g/10 minutes; and, a melt flow ratio(I₁₀/I₂) in the range of from 6 to
 10. 2. The polyethylene polymer ofclaim 1 having a haze per ASTM D1003 of less than 7%.
 3. Thepolyethylene polymer of claim 1 having a Gloss 20 per ASTM D2457 ofgreater than 106%.
 4. The polyethylene polymer of claim 1 having a Gloss45 per ASTM D2457 of greater than 76%.
 5. An article comprising thepolyethylene polymer of claim 1 wherein the article is selected from thegroup consisting of film, sheet, pipe, fiber, blow molded articles,injection molded articles, rotary molded articles.